This work aims to analyze and demonstrate the moral principles of Baron d’Holbach (1723-1789), mainly, how he bases the notion of happiness in his atheistic, fatalistic and eudemonistic materialism. At The System of Nature (or the laws of the physical world and the moral world), 1770, Holbach perceives that the unhappiness that plagues most human beings is caused by ignorance about the nature of which we are part of, as well as by the ignorance we have upon our own nature. By means of the experience that guides reason and provides the unveiling of nature and knowledge of its dynamics, Holbach believes that human behavior can be guided in the society life without dependence on theological dogmas. According to Baron, the very desire to be happy and to preserve oneself is a natural tendency in the human beings. And “the true happiness” will only be possible with a moral in accordance with the laws of nature and the natural needs of man, which require him the practice of a virtue that also considers the happiness of other human beings.